Tutorial by Examples: x

Create unique index

A unique index prevents the insertion of duplicated data in a table. NULL values can be inserted in the columns that form part of the unique index (since, by definition, a NULL value is different from any other value, including another NULL value) -- Creates a unique index for column 'name' in tabl...

MySQL • Indexes and Keys

Using Parent and Children scripts to execute code in parallel

child.py import time def main(): print "starting work" time.sleep(1) print "work work work work work" time.sleep(1) print "done working" if __name__ == '__main__': main() parent.py import os def main(): for i in range(5):...

Python Language • Parallel computation

Create a process and check its exit code

This example starts Notepad, waits for it to be closed, then gets its exit code. #include <Windows.h> int main() { STARTUPINFOW si = { 0 }; si.cb = sizeof(si); PROCESS_INFORMATION pi = { 0 }; // Create the child process BOOL success = CreateProcessW( L"C:...

Win32 API • Process and Thread Management

More flexibility with Popen

Using subprocess.Popen give more fine-grained control over launched processes than subprocess.call. Launching a subprocess process = subprocess.Popen([r'C:\path\to\app.exe', 'arg1', '--flag', 'arg']) The signature for Popen is very similar to the call function; however, Popen will return immedi...

Python Language • Subprocess Library

Killing Child Processes on Exit

Trap expressions don't have to be individual functions or programs, they can be more complex expressions as well. By combining jobs -p and kill, we can kill all spawned child processes of the shell on exit: trap 'jobs -p | xargs kill' EXIT

Bash • Using "trap" to react to signals and system events

Pow for faster exponentiation

Using the timeit module from the command line: > python -m timeit 'for x in xrange(50000): b = x**3' 10 loops, best of 3: 51.2 msec per loop > python -m timeit 'from math import pow' 'for x in xrange(50000): b = pow(x,3)' 100 loops, best of 3: 9.15 msec per loop The built-in ** operato...

Python Language • Math Module

Detect Whether Expression is Valid

It is possible to detect whether an operator or function can be called on a type. To test if a class has an overload of std::hash, one can do this: #include <functional> // for std::hash #include <type_traits> // for std::false_type and std::true_type #include <utility> // for s...

C++ • Metaprogramming

Generic Class Examples

A generic class with the type parameter Type class MyGenericClass<Type>{ var value: Type init(value: Type){ self.value = value } func getValue() -> Type{ return self.value } func setValue(value: Type){ self.value = value }...

Swift Language • Generics

encode/decode to hex no longer available

Python 2.x2.7 "1deadbeef3".decode('hex') # Out: '\x1d\xea\xdb\xee\xf3' '\x1d\xea\xdb\xee\xf3'.encode('hex') # Out: 1deadbeef3 Python 3.x3.0 "1deadbeef3".decode('hex') # Traceback (most recent call last): # File "<stdin>", line 1, in <module> ...

Python Language • Incompatibilities moving from Python 2 to Python 3

Creating custom exception types

Create a class inheriting from Exception: class FooException(Exception): pass try: raise FooException("insert description here") except FooException: print("A FooException was raised.") or another exception type: class NegativeError(ValueError): pass ...

Python Language • Exceptions

Iterating over a directory and filter by file extension

public void iterateAndFilter() throws IOException { Path dir = Paths.get("C:/foo/bar"); PathMatcher imageFileMatcher = FileSystems.getDefault().getPathMatcher( "regex:.*(?i:jpg|jpeg|png|gif|bmp|jpe|jfif)"); try (Direc...

Java Language • File I/O

Basic example of using requests and lxml to scrape some data

# For Python 2 compatibility. from __future__ import print_function import lxml.html import requests def main(): r = requests.get("https://httpbin.org") html_source = r.text root_element = lxml.html.fromstring(html_source) # Note root_element.xpath() gives a *...

Python Language • Web scraping with Python

Using expression in string literals

You can use curly braces to interpolate expressions into string literals: def f(x: String) = x + x val a = "A" s"${a}" // "A" s"${f(a)}" // "AA" Without the braces, scala would only interpolate the identifier after the $ (in this case f...

Scala Language • String Interpolation

Alternative loop syntax

You can also use loop with curly brackets like this: if ( have_posts() ) { while ( have_posts() ) { the_post(); var_dump( $post ); } }

WordPress • The Loop (main WordPress loop)

Initial Usage Example

jquery-ui-rotatable is a plugin for jQuery UI that works in a similar way to Draggable and Resizable, without being as full-featured. By default, it puts a small rotation icon in the bottom left of whatever element you want to make rotatable. <html> <head> <title>My Ro...

jQuery UI Library • jQuery UI Rotatable Plug-in

Complex Example - jQuery UI Dynamicly Create Dialog

Generally, dialog relies on a div within the HTML. Sometimes you may want to create a dialog from scratch, programmatically. Here is an example of a complex modal dialog created dynamically with interactive functions. HTML <div id="users-contain" class="ui-widget"> &lt...

jQuery UI Library • Dialog

Switch off properties during macro execution

It is best practice in any programming language to avoid premature optimization. However, if testing reveals that your code is running too slowly, you may gain some speed by switching off some of the application’s properties while it runs. Add this code to a standard module: Public Sub SpeedUp( _ ...

excel-vba • VBA Best Practices

Simple lambda expressions

// A simple adder function defined as a lambda expression. // Unlike with regular functions, parameter types often may be omitted because the // compiler can infer their types let adder = |a, b| a + b; // Lambdas can span across multiple lines, like normal functions. let multiplier = |a: i32, ...

Rust • Closures and lambda expressions

Lambdas with explicit return types

// lambda expressions can have explicitly annotated return types let floor_func = |x: f64| -> i64 { x.floor() as i64 };

Rust • Closures and lambda expressions

Sorting sequence containers using lambda expressions (C++11)

C++11 // Include sequence containers #include <vector> #include <deque> #include <list> #include <array> #include <forward_list> // Include sorting algorithm #include <algorithm> class Base { public: // Constructor that set variable to the va...

C++ • Sorting